An Update on Candida tropicalis Based on Basic and Clinical Approaches

Abstract

Candida tropicalis has emerged as one of the most important Candida species. It has been widely considered the second most virulent Candida species, only preceded by C. albicans. Besides, this species has been recognized as a very strong biofilm producer, surpassing C. albicans in most of the studies. In addition, it produces a wide range of other virulence factors, including: adhesion to buccal epithelial and endothelial cells; the secretion of lytic enzymes, such as proteinases, phospholipases, and hemolysins, bud-to-hyphae transition (also called morphogenesis) and the phenomenon called phenotypic switching. This is a species very closely related to C. albicans and has been easily identified with both phenotypic and molecular methods. In addition, no cryptic sibling species were yet described in the literature, what is contradictory to some other medically important Candida species. C. tropicalis is a clinically relevant species and may be the second or third etiological agent of candidemia, specifically in Latin American countries and Asia. Antifungal resistance to the azoles, polyenes, and echinocandins has already been described. Apart from all these characteristics, C. tropicalis has been considered an osmotolerant microorganism and this ability to survive to high salt concentration may be important for fungal persistence in saline environments. This physiological characteristic makes this species suitable for use in biotechnology processes. Here we describe an update of C. tropicalis, focusing on all these previously mentioned subjects.

Keywords: Candida tropicalis; antifungal resistance; phenotypic and molecular identification; update; virulence factors.

Figure 1

Phenotypic characteristics of Candida tropicalis. (A) Cream-colored, dull, smooth colonies, after 48 h of incubation at 30°C on Sabouraud dextrose agar; (B) Colonies with typical dark blue color on CHROMagar Candida® medium after 96 h of incubation at 35°C; (C) Micromorphological aspects after incubation in YPD medium containing 20% fetal bovine serum (FBS) for 7 days at 30°C, 400x: blastoconidia in single or branched chains, true hyphae and abundant pseudohyphae.

Figure 2

Phylogenetic tree of Candida spp. internal transcribed spacer 1 (ITS1)-5.8S ribosomal RNA gene and internal transcribed spacer 2 (ITS2) complete sequences and their accession numbers, obtained from Genbank database at https://www.ncbi.nlm.nih.gov. Sequences were aligned using BioEdit software (v7.2.61). Aligned sequences were used for phylogenetic analysis conducted with Mega 7.0.26 Software. The method used for tree constructions was maximum parsimony. Phylogram stability was accessed by bootstrapping with 1,000 pseudoreplications.